Marquzz wrote:

Got this motherboard sent to me by a friend. This is little too old for me and I'm lost at this tech. Could anyone shed some light on what this is and if it's worth fixing. Where can I get components needed if I decide to fix it?

I imagine he is quite a good friend then?... if only my friends donated their old 386 mobo's from time to time.

It looks to be a pretty fast 386 board... with a fixed 40MHz frequency crystal oscillator, UMC 491F chipset, 128Kb (8 x 32K) 20ns cache / 15ns Tag, and a socket for a 387.

Yea... i'd say it's worth servicing. It looks like you may need to solder a few jumpers between points around where the battery used to be. The bios pins have not discoloured or anything and still chromed so the damage doesn't seem too extensive. You may not need any extra parts either apart from 0.5 - 1mm copper wire... and a soldering kit (if you don't already have one).

This board would make a sweet 386 system build.

I didn't say he gave it to me, just wanted me to take a look. But he's not into this old stuff so I don't know if he wants it back either 😉

So, there are a few things that needs to be exchanged. Do you have any place, in Europe preferably, where I can get capacitors like this? Any tip on how to fix the erroded tracks? Could you specify what needs to be done with the jumpers you mentioned?

Any suggestion on 387 processor? What cards do you recommend to get, Video, sound, controller cards, (mouse?). Is there anything I need to think about when getting RAM? My knowledge starts at Socket 7, so this is basically a gray zone for me 😀

Still, if people I know were sending me 386 motherboards... I wouldn't be complaining, especially if they are not sure they want their parts back! 😁

You want to replace the caps? From the view above they seems ok... i.e. not needing changed. They may spell a different picture if you have a planner view i.e. from the side... but the few I can see, they are not bulging or about to pop... if that is the same with the rest, I'd leave them. The tracks are an easy fix... just get 0.5 to 1mm copper wire as I said earlier and solder (using shortest length of wire possible) between where the track starts and ends... so the eroded track is completely bypassed.

For a 387 you have a couple of choices Cyrix is most popular but ULSI were manufactured last. Regarding cards, it depends on what you are going to do with the system. For sound cards, everyone is different... as certain sound cards sound different from others... there are many threads here on Vogons and many comparison videos on youtube covering the subject... it comes down to which sound you prefer from whichever card. If you are not an Audiophile... a regular old Soundblaster will do.

Video cards on ISA will not have much between them as they are all bottlenecked by the bus in any case... but again, it depends on what you're going to do with the system i.e. will it be a Dos machine / or for Windows? Dos, any Cirrus Logic will do (CL5434) if you can find one... and that will pretty much cover Windows too. Otherwise any ISA VGA card with an accelerator will do for Windows.

RAM, 30 pin simms in groups of 4 sticks i.e. 8 bits per stick x 4 = 32 bits wide, all the same size and parity (4 x 1Mb, 4 x 4Mb etc).

My bad, I missed that single ceramic disk cap near where the battery was.

I don't think these are polarized so that would make the job a little easier... rs components (http://uk.rs-online.com/web/) is what I use here in the UK. I don't know if they have a shop in Sweden, or there is Maplin for individual parts.

If you have a good camera on your phone... take a close-up picture of the other ceramic disk cap near to the one that has blown for their values. Post the picture here and I'll translate the code for you and let you know which is required i.e.. specification... but in all, you're talking nano-Farads.

Edit; - Also, if you get some vinegar and a toothbrush to get rid off the erosion before you work on it... it'll be clearer to see how many / all the jumpers you'll be needing

First of all, I suggest you to go and find some information about what you really have. https://th99.bl4ckb0x.de/ might help. I can't see any distinguishing printings or labels on your board from the photos, but you can try matching the layout of your board with the board pictures on that site.

The second thing is, you don't have a CMOS battery (it has been removed - which is a nice thing), but not before it leaked and corroded some copper lines (which is not good) so you might be in need of some repair for those greened copper lines. Actually I can't see an external battery connector on the board, so you might also be in need of connecting a coin battery to the board, which is well documented around the net.

I think before going into that kind of repair job, you need to see if the board boots at this condition. CMOS battery does not matter at this point, it should boot without one. For this, the minimum requirements are a display card (mid level 16 bit ISA VGA cards are aplenty in ebay and relatively cheap - you can use any VGA display with it, including your current super modern one) and some RAM. You need 30 pin SIMM RAM and you need at least 4 of the same (they must be used in groups of four). They are also available in ebay, and you can still find new ones from OWC computing (only in 16MB modules, and you need to buy 4 of them)

The one thing you need to use it properly is of course an ISA 16 bit multi I/O card, which will have al least one IDE and one floppy port, and also have some parallel/serial ports and even a game port. Generic ones are cheaply available thru ebay again, but there are so generic, I suggest to find one with a printed/silk screened jumper setting instructions on it or one that came with a instruction sheet. If this would not be the case, you can also utilize the above web site for it.

For HDD, you can try to find a small old IDE, you can choose to go with a CF card (with super cheap CF to IDE adapters), or you can use your modern SATA DISK with IDE to SATA adapters. Be sure that your BIOS most probably cannot accept any drive larger than 512MB, and you need to overcome this by using an overlay software driver or formatting the big drive using something like Seatools.

A common keyboard with a PS/2 to AT adapter will work, but you basically need to forget about PS/2 mouse. A serial mouse is still something you can obtain from ebay for relatively cheap prices. If you insist on PS/2, there are solutions around, but not an easy one available yet.

For other things (sound card, NIC, floppy, CD-ROM, etc.) you just need to use standard stuff, nothing special is needed (as long as all the cards would be ISA of course)

tayyare wrote:

I think before going into that kind of repair job, you need to see if the board boots at this condition.

There are 'open circuits' (OC's) there and a blown capacitor... it is almost a certainty that it's not going to boot.

Looking at the 2nd picture... next to the silk-screened positive sign "+" ... the tracks are wide open, and they look to be the power lines for the whole ISA bus... meaning no power to the ISA bus = no VGA, no VGA = no boot!

The job needing done first is to clean those tracks (continuity test to confirm OC's) and soldering wire (jumpers)... likely from the AT power connection directly to the power points on the 1st ISA slot.

If you jump the power to the 1st ISA slot... the whole ISA bus and all the ISA slots will have power.

Then you may get it to boot, if not, it'll be that ceramic disk cap.

386_junkie wrote:

tayyare wrote:

I think before going into that kind of repair job, you need to see if the board boots at this condition.

There are 'open circuits' (OC's) there and a blown capacitor... it is almost a certainty that it's not going to boot.

Looking at the 2nd picture... next to the silk-screened positive sign "+" ... the tracks are wide open, and they look to be the power lines for the whole ISA bus... meaning no power to the ISA bus = no VGA, no VGA = no boot!

My bad, didn't check the pictures long enough. I couldn't even spotted the blown cap, before you mentioned it. Just seen some greening and assumed it might be still ok.

Great! Thanks for all the informations! Didn't know there were multi I/O cards, thats perfect, need to find one of those, and of course a ISA video card. The blown capacitor is 47uF I think since that's the number on the ones that looks good.

I have a AT keyboard and a serial mouse. If I decide to build something useful from this it will probably be a Dos 6.22 / Win3.11 machine since that's the earliest I remember (I got more into hardware around SS7). Will probably play some games from this era, like Stunts, Duck Tales and Pinball Fantasies.

There are good tricks to repair those bad copper traces.. First i would recommend to make pictures of that contaminated environment, so you know where to put the got parts back in the board.. Then remove anything on that area.. Clean the board with vinegar, so the acid will neutralize.
Then clean everything, scrap the bad traces away and leave the good one behind.. If you have some fine copper bread and epoxy glue you can lay a new part of traces in.. With kapton tape you can hold the new traces on the board.. When the epoxy glue is hardened, solder the ends together.

There is also some epoxy glue available for covering the top part of the trace.. If you have some patience, the board can look is new again..

Between the CPU and the UMC chip there is an area where it looks like a socket could be placed, with enough pins that makes me think it could even be a socket for a 386. Why is it there?

vladstamate wrote:

Between the CPU and the UMC chip there is an area where it looks like a socket could be placed, with enough pins that makes me think it could even be a socket for a 386. Why is it there?

The place for a socket is there because the manufacturer likely sold another version of the same board without the soldered 386 DX40 but with a 386 socket instead.

I even have a board with both a soldered CPU and a socket and you can chose between them with a few jumpers.

Marquzz wrote:

The blown capacitor is 47uF

This sounds a little high... does it have this writing exactly, and do you have a clear picture of it?

Sometimes with such small caps they have a number... then another number to determine how many "0's" to add after that number to determine if it's pico, nano, or micro... either this or it's letters.

386_junkie wrote:

Marquzz wrote:

The blown capacitor is 47uF

This sounds a little high... does it have this writing exactly, and do you have a clear picture of it?

Sometimes with such small caps they have a number... then another number to determine how many "0's" to add after that number to determine if it's pico, nano, or micro... either this or it's letters.

I've attached more images

Marquzz wrote:

386_junkie wrote:

Marquzz wrote:

The blown capacitor is 47uF

This sounds a little high... does it have this writing exactly, and do you have a clear picture of it?

Sometimes with such small caps they have a number... then another number to determine how many "0's" to add after that number to determine if it's pico, nano, or micro... either this or it's letters.

I've attached more images

You should use some vinegar to neutralize the battery "acid" and remove the corrosion, then clean the board with isopropanol. The busted cap is likely the same value as its friends nearby.

When fixing the board is often better to solder new wires directly from A to B instead of trying to fix the broken trace between A and B. Im no expert when it comes to this but many of my old 286, 386 and 486 motherboards have such fixes.

The small bead caps reading 4Z, then 10 under... are 0.1uF (micro farads). 10 is the rating, 4 is the multiplier and Z is the tolerance. So... to get your value; -

0.000,000,010 = 10pF (pico)
x 4 =
0.000,100,000 = 100nF or 0.1uF (micro)

_______________________________________________________________

Now, the flat round disc's (the blown cap) have only 2 digits... "47", meaning 47pF (pico).

The third digit if it existed would be like the "4" in the previous example above.. the multiplier. The underline is the voltage rating... for PCB's you'll not need move than a 50v cap.

As there is no 3rd digit... all you need is a 47pF ceramic disk cap replacement rated at 50 volts.

I just realized that I have not commented on your FPU/mathco question. I believe anything that work at 40MHz will happily work on your board. There are Cyrix, IIT, Intel and Ulsi ones around. But in reality, as long as you will not go into something like CAD, FORTRAN compiling, and/or anything related with maths and sciences software (that requires floating point calculation by design) in that machine (I believe you won't), that FPU will sit there doing nothing.

To say the truth, I have two 386 class machines and both have their FPU installed. 😊

http://wiretap.area.com/Gopher/Library/Techdo … /Cpu/coproc.txt